"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
iOS 7.1 Improves Performance for iPhone 4 Users
Today, with the release of iOS 7.1, Apple has much improved the experience of iPhone 4 users on iOS 7, though not entirely back to what users saw in iOS 6.1.3. According to Ars Technica, there is a measurable improvement in iOS 7.1 across a number of native iOS apps, including the speed at which the apps open from the home screen:
There's a measurable improvement over iOS 7.0 across all of these apps, some more noticeable than others. In a few instances, iOS 7.1 very nearly catches up with iOS 6.1.3, which is impressive given the gap between the two operating systems in some of these apps. It's not a complete recovery from the original iOS 7.0 release, but it's about as good as Apple can do with hardware this old. The small speed improvements are present throughout the operating system, and this makes the iPhone 4 feel more responsive than it did, if not always as responsive as it once was.As Ars notes, iOS 7.1 may well be the final major iOS release for the iPhone 4, as Apple generally removes support for the last generation of iPhones when it releases a new operating system each year. Ars says iOS 7.1 makes the experience good enough that using the iPhone 4 is no longer "unbearable", but that there are "unmistakable" benefits to moving to a faster phone.
iOS 7.1 also helps with the UI jerkiness that was all over the place in 7.0. It's easiest to capture the difference in video—actions like launching apps or pulling up the Control Center shade are always visibly jerky in iOS 7.0, but they're smooth (or at least smoother) in the new update.